The present invention relates to a method and apparatus for the transportation of hazardous wastes in which the hazardous waste includes both solid and liquid components mixed together. The invention provides for thorough mixing of the solid and liquid components with numerous pertinent advantages.
As people and companies become more and more attuned to the appropriate disposition of hazardous waste, whether by personal desire or government regulation, the need arises for finding suitable ways of handling these wastes, so that the disposition can be effectuated safely and economically.
A particular class of hazardous waste has a high volatility and combustibility, making it dangerous to handle but useful as a fuel. An example of this type of waste is generated by the painting process. Leftover paints, paint thinners, paint solvents, and paint cleaning compositions are mixed together to yield a mixture which has these characteristics and which is toxic when released to the environment. An industry has arisen to use these paint-related wastes as fuel in industrial burners, most particularly in cement kilns. The kilns burn the solid and liquid waste as part of the burner fuel, and the ash residue of the combustion process serves as clinker in the cement. The high temperature in the kiln safely decomposes the various components of the paint-related residue to benign discharges. In addition, many of the solvent components of the waste are recyclable by removal from the waste by distillation. This reduces the volume of the waste, but increases the proportion of solids.
However, the kilns involved are located at some distance from the origin of the waste or the place of distillation, so a need arises to transport the waste to the kiln. Since the waste is highly combustible, transportation of the waste, by United States Department of Transportation regulations, must be in tank trucks having special construction. The applicable standard is Department of Transportation Hazardous Waste MC 307, which includes requiring that the empty tank not leak when subjected to an air pressure of 1.76 kilograms per square meter, so that the structural integrity of the tank must be substantial. Any breach of the wall of the tank requires retesting of the tank to its MC 307 rating. The entire text of the Department of Transportation MC 307 standard is incorporated herein by reference.
At the completion of the trip to the kiln, the discharge of the hazardous waste from the tank to the kiln burner or a holding tank at the kiln has previously been problematic. The liquid successfully drains from the tank, but a large quantity of the solids remain. Previous attempts to deal with this problem include providing drop centers or drop bellies in the tanks so that the bottom wall of the tank is sloping, and gravity assists in the discharge of solids along with the liquids. This design has met with only limited success.
The retention of solids in the bottom of the tank poses numerous disadvantages. First, the backhaul of the tank to pick up another load entails hauling the solids back to the pickup point, making the tank heavier and wasting fuel. Of course, the buildup of the solids reduces the capacity of the tank so that each subsequent refill of the tank includes less and less volume. Typically, two inches of solids were deposited in the bottom of the tank from each load prior to the use of the present invention.
Also, the solids have a high BTU level, so that they contribute to the fuel value of the hazardous waste when they are adequately discharged with the liquid. For them to remain deposited in the bottom of the tank diminishes the available fuel value of the waste.
Moreover, the proper operation of the kiln requires the proper mix of components in the hazardous waste when used a fuel, including maximum allowable levels of chloride and water, and other components. Not only are the solids capable of precipitating from the mixture, but some of the liquids in the mixture are not entirely miscible. These liquids can separate, causing the liquid as discharged from the tank to have different fuel values, depending on which portion of the tank is being drained at any given time. This can be disruptive to proper operation of the kiln or proper complete combustion of the waste so that the kiln""s discharges fall outside of permissible or desired ranges. As a result, the kiln operator tests each load of waste and sometimes turns away a load found not to meet its specifications.
Some such tests have been erroneous in that only a certain fraction of the overall volume of hazardous waste was sampled because of the separation of components. Although the overall mixture in the tank may be within the parameters set by the kiln, the precise sample taken by the kiln tester may fall outside these parameters and result in rejection of the entire truckload.
Typically, the buildup of the solids in the bottom of the tank has been dealt with by having a workman enter the tank with a shovel to shovel the solids into barrels for processing. Such processing, rather than being a useful disposition of the solids as in burning in the kiln, constitutes underground storage or wasteful incineration. This does not, of course, solve the problems of incomplete mixing of liquids and is not a chore the workman typically enjoys. It is known that a previous attempt to agitate the contents of a hazardous waste transport tank included the use of vertically extending augers or the like, but it resulted in a considerable residue of solids in the tank after it was supposedly drained. While other types of tanks in which agitators are provided are known, such as concrete mixers and the like, none are designed for the hauling of hazardous waste under conditions meeting Department of Transportation MC 307 standards.
Thus, the settling of the contents of the tanks has posed numerous problems, which prior art attempts to rectify have not been successful in alleviating. Accordingly, there is a need in the art for a method and apparatus for agitating the hazardous waste solids and liquids to maintain them in flowable form so that they may be fully and usefully discharged from the tank.
The present invention fulfills this need in the art by providing an apparatus for holding hazardous waste made up of solids and liquids in a flowable form including a tank made of material selected to be impervious to and non-corrodible by the hazardous waste and having a non-critical portion, an agitator in the tank having fluid agitation portions oriented for rotational movement about a horizontal axis, a non-sparking motor located within the tank connected to the agitator for imparting rotation to the fluid agitation portions, and a power source for the motor outside the tank having means passing through the non-critical portion of the tank for communicating power from the power source to the motor. Thus, the power source may communicate power to the non-spark generating motor to impart rotation to the agitator to cause the fluid agitation portions to agitate hazardous waste made up of solids and liquids held in the tank to maintain the hazardous waste in flowable form.
Preferably, the agitator includes support elements for the fluid agitation portions located completely within the tank, and the support elements include bronze bearings in which the fluid agitation portions may rotate. Desirably, the tank has a central horizontal axis, and the horizontal axis about which the fluid agitation portions are oriented is parallel and substantially below the central horizontal axis. The fluid agitation portions include an array of axially extending blades. The blades extend at a slight angle to the axis of rotation so that upon rotation of the blades, the solids component of the hazardous waste is transported axially.
Preferably, the tank meets United States Department of Transportation Hazardous Waste transport standard MC 307. The tank is stainless steel, and the agitator is aluminum. The agitator may also be made of stainless steel or other suitable material.
In one embodiment, the tank has a rear discharge port and the blades transport the solids component to the rear discharge port. In another embodiment the tank has a drop center discharge port and the agitator includes a first set of blades aft of the discharge port and a second set of blades forward of the discharge port. The blades transport the solids components to the center discharge port. In this embodiment, the tank may have a forward floor portion slanted rearwardly forward of the discharge port and an aft floor portion slanted forwardly aft of the discharge port. Desirably, the first set of blades is oriented for rotation about an axis substantially parallel with the aft floor portion, and the second set of blades is oriented for rotation about an axis substantially parallel with the forward floor portion.
The non sparking motor may be a hydraulic motor, the power source a hydraulic fluid pump, and the means for communicating power a pair of hydraulic lines. The non-critical portion of the tank is a manway collar, and the hydraulic lines pass through the manway collar.
In one embodiment, the tank is mobile. In this embodiment the apparatus may include a truck or trailer body on which the tank is mounted. Alternatively, it may include a rail car body or a ship, barge or boat on which the tank is mounted.
In another embodiment (which may also be mobile) the tank has a plurality of compartments, and one of the agitators is located in each of the compartments. This permits a plurality of mixtures of hazardous waste to be held in the tank without mixing between the mixtures, but with each mixture held in a flowable form.
The invention also provides a method of transporting hazardous waste composed of solids and liquids including the steps of: depositing the hazardous waste in a United States Department of Transportation MC 307 rated tank, moving the tank of hazardous waste to a destination, agitating the hazardous waste to maintain the hazardous waste in substantially completely flowable form without appreciable solids deposition, and discharging the flowable hazardous waste to a suitable repository. The agitation step includes introducing rotational motion to the fluid about a horizontal axis. Desirably, but not necessarily, the agitation step occurs simultaneously with the moving step.
The invention also provides a method of maximizing the available fuel value of a combustible hazardous waste mixture of solids and liquids, each of the solids and liquids being independently combustible, including the steps of: holding the hazardous waste in a tank, agitating the hazardous waste while it is in the tank so that the solids and liquids are in the form of a flowable mixture of independently combustible solids and liquids, and discharging the flowable mixture of independently combustible solids and liquids from the tank to a burner for combustion, whereby both solids and liquids are available to the burner for combustion. In one embodiment this method also includes the step of providing paint residues, paint thinners, paint cleaning solvents or the distillation residue thereof as the combustible hazardous waste. The materials to be hauled may be various, including foods, petroleum distillates, oils and other materials.